One stop for end mill speed and feed
An end mill needs two numbers set correctly: how fast it spins and how fast it travels. This calculator does both at once — it turns your material cutting speed and cutter diameter into spindle RPM, then multiplies by chip load and flute count to give the table feed. Dial these in and the cutter throws clean chips instead of dust.
The formulas
Spindle speed: RPM = (SFM x 12) / (pi x D) imperial, or (Vc x 1000) / (pi x D) metric, with D the end mill diameter. Table feed = RPM x chip load per tooth x number of flutes. Feed per revolution is chip load times flute count.
How this relates to the other tools
This is the milling counterpart to the drill speed calculator. It rolls the RPM calculator and the feed rate calculator into a single end-mill workflow, so you do not have to copy a number between them.
Typical carbide milling speeds
| Material | Speed (SFM) | Chip load, 1/2 in (in/tooth) |
|---|---|---|
| Aluminum | 600 – 1000 | 0.004 – 0.006 |
| Brass / bronze | 400 – 600 | 0.002 – 0.004 |
| Mild steel | 350 – 450 | 0.002 – 0.003 |
| Stainless steel | 150 – 250 | 0.001 – 0.002 |
Worked example
A 1/2 inch 4-flute carbide end mill in mild steel at 400 SFM with 0.002 in chip load: RPM = (400 x 12) / (pi x 0.5) = 3056, and feed = 3056 x 0.002 x 4 = 24.4 IPM.
FAQ
Should I scale chip load for small cutters?
Yes. Chip load roughly tracks diameter, so a 1/8 inch end mill takes a much lighter chip than a 1/2 inch one. Start light on small tools and listen for a clean cut.
What is chip thinning?
At light radial cuts (well under half the diameter) each tooth takes a thinner chip than the feed implies, so you can and should feed faster to keep the chip in range. For full-width slotting, the straight formula above applies.